package 笔试.度小满;

import java.util.Arrays;
import java.util.Scanner;

public class Demo1 {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int k = sc.nextInt();
        int[] nums = new int[n];
        for (int i = 0; i < n; i++) {
            nums[i] = sc.nextInt();
        }
        Arrays.sort(nums);
        int fenmu = n*(n-1)/2;
        //要 long fenmu = n*(n-1)/2;
        int fenzi = 0;
        for (int i = 0; i < n; i++) {
            for (int j = i+1; j <n ; j++) {
                if(nums[j]-nums[i]<=k){
                    fenzi++;
                }else{
                    break;
                }
            }
        }
        if (fenzi==0){
            System.out.println(fenzi+"/"+fenmu);
        }else{ //化简分数
            int c = GCD(fenzi,fenmu);
            System.out.println(fenzi/c+"/"+fenmu/c);
        }
    }

    //化简分数
    public static int GCD(int a,int b){
        if(b==0){
            return a;
        }else{
            return GCD(b,a%b);
        }
    }
}
